1. Field of the Invention
The present invention relates to a scanner apparatus and an image recording apparatus provided with an array-like light source, and particularly to an image recording apparatus provided with an array-like light source having high scanning accuracy and an image recording apparatus provided with an array-like light source which suppresses a variation of a beam diameter caused by deviation of focal position without using an autofocus mechanism to realize image recording of high quality and high density at high speeds.
2. Description of the Related Art
For making the recording speed of an image recording device higher, there has been studied an image recording apparatus for driving an array-like light source according to a recorded image pattern, without using a polygon mirror, which has a limitation in making its rotational speed higher, to thereby exit a plurality of light beams.
A conventional image recording apparatus provided with an array-like light source as described is disclosed, for example, in Japanese Published Unexamined Application No. Sho 64-42667. This image recording apparatus has the constitution in which a surface emission laser array is arranged in the vicinity of a photosensitive drum to directly expose the photosensitive drum. It is contemplated that according to this image recording apparatus, the surface emission laser array is driven at high speeds, and the photosensitive drum is driven at rotational speeds according to the driving speed of the surface emission laser array to obtain high speed image recording.
Further, a conventional laser array scanner provided with an array-like light source is disclosed, for example, in Japanese Published Unexamined Patent Application No. Hei 1-152683. This laser array scanner comprises a semiconductor laser array having a plurality of semiconductor lasers disposed in a row, and optical means, a convex lens having a larger diameter than the length of the semiconductor laser array so as to include all the light emitting portions of a plurality of semiconductor lasers. It is contemplated that according to this laser array scanner, when the semiconductor laser arrays are driven at high speeds, the high-speed scanning can be realized.
However, according to the conventional image recording apparatus and laser array scanner provided with an array-like light source, deviation in a focal position occurs depending on change in temperature, accuracy of mounting, accuracy of parts, vibrations, etc. so that abeam diameter varies. Accordingly, the image recording of high density, 1200 dpi, demanded recently, cannot be carried out with high quality and at high speeds.
On the other hand, it is reported in J. Opt. SOC. Am. A, Vol. 4, No. 4/April 1987, P651 to P654, and Optics Communications, Vol. 64, No. 6/Dec. 15, 1987, P491 to P495 that the laser beam having a light-intensity distribution of the 0 order Bessel-Gaussian type is larger in its focal depth than that of a Gaussian type.
As a method for forming a laser beam of the 0 order Bessel-Gaussian type, the former reference discloses a method in which an annular slit is placed in a collimated laser beam, and a light beam coming out thereof is subjected to Fourier conversion to thereby increase resolution of the laser beam.
However, according to the conventional image recording apparatus and laser array scanner provided with an array-like light source, since a plurality of laser beams are emitted to a space region corresponding to the length in a main scanning direction of the semiconductor laser arrays, it is difficult to practically ensure that (1) the respective laser beams are collimated and (2) Fourier conversion elements are arranged in the collimated laser beams to equally increase the focal depth of the laser beams. Further, according to the conventional laser array scanner provided with an array-like light source, since the light beams coming from the end of the semiconductor laser arrays are incident with a large incident angle with respect to an optical axis of the convex lens, the quantity of light of the light beams is reduced, and the beam diameter varies.
Therefore, it is necessary that an image forming optical system be arranged between the semiconductor laser array and the scanning surface, and the deviation in a focal position is corrected by an autofocus mechanism. However, since this autofocus mechanism cannot detect the beam diameter at the scanning surface, the light beams are to be branched and detected, giving rise to some problems such that the accuracy is not high, or the like.